Method of producing a composite pipe and such a composite pipe

ABSTRACT

A composite pipe comprises a polyetheretherketone innermost pipe around which a reinforcing overwrap is arranged. A protective sheath surrounds the overwrap. Such a composite pipe may be made by selecting a polyetheretherketone pipe having an outer region having a crystallinity of less than 25%; overlaying the selected pipe with overwrap; and subjecting the combination to heat, thereby causing the crystallinity of the outer region of the polyetheretherketone pipe to increase. The method reduces the risk of pipe failure.

This invention relates to a pipe and particularly, although notexclusively, relates to a method of producing a composite pipe and sucha pipe per se. Embodiments aim to extend the lifetime and/or reduce therisk of premature failure of a pipe which may carry a high pressurefluid (e.g. liquid (optionally containing particulates), gas or amixture of the two) and/or be subjected to high external forces, in use.Preferred embodiments relate to pipes for use in the oil and/or gasindustries for example flexible risers arranged to transport fluidsbetween floating production units and a sub-sea wellhead.

Composite umbilicals and other composite pipes for use in the recoveryof hydrocarbons from oil or gas wells or for use in performing downholeoperations are well-known, for example from US2002/0007970, U.S. Pat.No. 6,761,574, WO2006/071362, U.S. Pat. No. 6,538,198, WO99/67561 andWO2006/059220.

In general terms, a composite pipe may comprise an inner pipe which maybe arranged to carry pressurized oil, gas or other fluids (e.g. mixturesof liquids and gases), surrounded by a reinforcing means. In some cases,for example in umbilical tubes/pipes the pressure within the compositepipe may be as high as 30000 psi; in other cases, for example in risersfor transporting oil/gas upwards from a subterranean formation, thepressure, whilst still appreciable, may be less than 8000 psi.

Known inner pipes of composite pipes may comprise a polymeric material,for example a polyamide, polyvinylidene fluoride,fluoroethylene-propylene, other fluoropolymers or polyetheretherketone.The inner pipe needs to be thermally and chemically resistant and robustunder the conditions of temperature and pressure to which it may besubjected by fluid flowing through it in use. The reinforcing means maycomprise one or more layers around the inner pipe which are arranged toresist expansion of the inner pipe due to the pressure of fluid flowingtherewithin, and to protect the inner pipe from external pressure andmechanical and thermal loads to which the pipe may be exposed in use.The reinforcing means may comprise a reinforcing tape which is woundaround the inner tube and optionally glued or welded thereto. Thereinforcing tape may comprise fibrous material, such as carbon, glass oraramid fibres, embedded in a thermoplastic or thermosetting resin suchas a polyamide, polysulphone, polyetherimide, polyethersulphone orpolyetheretherketone.

It is of course desirable for composite pipes to have the maximumpossible useful lifetimes. However, composite pipes may be manufacturedwith high internal stress (for example due to the pipes havingsignificantly different levels of crystallinity across their wallthickness) which may lead to premature failure of the pipes, in use. Forexample, when a composite pipe comprises an inner pipe around which iswound a tape which is not bonded to the inner pipe, there may be a smallamount of play between the inner pipe and tape. In use, when the innerpipe transports a pressure fluid, the inner pipe may expand slightly andthen contract as the pressure of the fluid reduces and/or flow of fluidis periodically stopped. This expansion and contraction of the innerpipe may cause fatigue in the inner pipe and cause it to fail forexample by cracking or otherwise being rendered less effective.Composite pipes which comprise tape welded to the inner pipe may also beinherently stressed such that, when such a composite pipe is subjectedto pressure and/or movement (e.g. flexing or tension caused by the forceof the sea) such force may become concentrated in certain stressedregions and, consequently, the composite pipe may fail in such regionsprematurely.

It is an object of the present invention to address the aforementionedproblems.

It is an object of a preferred embodiment of the present invention toprovide a composite pipe with reduced internal stress.

According to a first aspect of the invention, there is provided a methodof producing a composite pipe which comprises:

(i) selecting a pipe P1 having an outer region comprising a crystallineor crystallisable polymeric material having a crystallinity of less than25%, wherein said polymeric material includes:

(a) phenyl moieties;

(b) ether and/or thioether moieties; and, optionally,

(c) ketone and/or sulphone moieties;

(ii) overlaying the selected pipe P1 with a reinforcing means andcausing the crystallinity of the outer region of pipe P1 to increase,thereby to define the composite pipe.

FTIR may be used to assess crystallinity and this may be used to assessthe level of crystallinity at a surface and/or across the thickness of asample. Reference is made to a paper titled “Crystallinity inPoly(Aryl-Ether-Ketone) Plaques Studied by Multiple Internal ReflectionSpectroscopy” (Polymer Bull, 11, 433 (1984)).

Said crystallinity of the outer region in step (i) may be less than 21%,is suitably less than 18% and, preferably, is less than 15%. In somecases, said crystallinity may be less than 14%, 13%, 12%, 11% or 10%.The crystallinity may be greater than 5%, 6% or 7%. Suitably, thecrystallinity of the outer region may be assessed by measuring thecrystallinity of an outer surface of pipe P1, for example by FTIR asdescribed.

Said pipe P1 suitably has a substantially circular cross-section. Saidouter region is preferably defined by a substantially annularcross-section region. Said pipe suitably includes an annular wall,wherein said outer region comprises an annular region defining theperiphery of the annular wall. Said outer region having saidcrystallinity referred to preferably extends across at least 90% of thearea of the periphery of the annular wall. Said outer region having saidcrystallinity preferably extends substantially along the entire extentof said pipe. Thus, preferably, substantially the entirety of theperiphery of the pipe, for example, the entirety of a circularlycylindrical surface of the pipe, has said crystallinity. Thus, suitably,the crystallinity may be assessed using the FTIR method described, atany position on a radially outwardly facing surface of the pipe P1.

Said pipe P1 may have an outside diameter of at least 2.5 cm, suitablyat least 7 cm, preferably at least 10 cm, more preferably at least 15cm. The diameter may be less than 50 cm, preferably less than 40 cm,more preferably less than 30 cm.

The thickness of the wall which defines the pipe P1 may be at least 0.5mm, suitably at least 0.8 mm, preferably 1 mm or more. The thickness maybe less than 30 mm, suitably less than 15 mm, preferably less than 10mm, more preferably less than 8 mm, especially less than 6 mm. Thethickness is preferably in the range 1 mm to 5 mm.

In some cases, however, the outside diameter may be up to about 100 cm,especially where relatively short pipe lengths are provided.

Said outer region may have a thickness of at least 50 μm or at least 100μm. It may be 250 μm or less. The thickness is suitably dependent on thecooling regime, for example the coolant temperature and time of contactwith coolant. Typically, it may be about 250 μm where the coolant iscold water and the immersion time is such as to bring about a sufficientreduction in temperature whilst ensuring any residual heat does not leadto annealing of the outer region.

The ratio of the thickness of the outer region to the thickness of theannular wall which defines pipe P1 may be in the range 0.01 to 0.2, forexample in the range 0.025 to 0.1.

An inside surface of the pipe (e.g. a radially inwardly facing surface)which is suitably defined by an inwardly facing surface of the annularwall, preferably has a crystallinity which is greater than thecrystallinity of said outer region, suitably by at least 2%. Thecrystallinity of said inwardly facing surface may be at least 4%,suitably at least 6%, preferably at least 8%, more preferably at least10% more than the crystallinity of the outer region of pipe P1 selectedin step (i) of the method. The crystallinity of said inwardly facingsurface may be at least 25%, or at least 27%, or at least 30%. The ratioof the crystallinity of the outer region, for example an outer surfaceof pipe P1, to the crystallinity of said inside surface of pipe P1 maybe in the range 0.2 to 0.8.

The crystallinity of the inside surface of pipe P1 may not be themaximum crystallinity of a region of the pipe. In this regard, asillustrated in FIG. 4 hereinafter, the maximum crystallinity may befound slightly radially outwardly of said inside surface. Thus, themaximum crystallinity in a region of said pipe P1, suitably measured byFTIR, is suitably greater than the crystallinity of said outer region,suitably by at least 2%. The maximum crystallinity may be at least 4%,suitably at least 6%, preferably at least 8%, more preferably at least10% more than the crystallinity of the outer region of pipe P1 selectedin step (i) of the method. The maximum crystallinity may be at least25%, 27% or 29%. In some cases, it could be as high as 35%. The ratio ofthe crystallinity of the outer region, for example an outer surface ofpipe P1, to the maximum crystallinity of pipe P1 may be in the range 0.2to 0.8.

Said pipe P1 preferably comprises, more preferably consists essentiallyof, a single said polymeric material or a single homogenous polymericcomposition comprising said polymeric material. Thus, said pipe P1 ispreferably substantially homogenous except that it comprises a polymericmaterial having different levels of crystallinity between its inner andouter surfaces, for example between the outer region and an insidesurface of the pipe.

Said polymeric material is suitably semi-crystalline and may be suchthat the kinetics of crystallisation are so fast that it issubstantially impossible to produce a solid from the polymeric materialwhich is fully amorphous. For example, the crystallinity half-life(t_(0.5)) of the polymeric material at 15° C. above its Tg may be lessthan 1000 seconds, less than 500 seconds, less than 250 seconds, or lessthan 150 seconds determined in accordance with the description in J.Brandrup, E. H. Immergut and E. A. Grulke, Polymer Handbook 4^(th)Edition, Wiley Interscience, 1999, ISBN 0-471-47936-5 (Vol 1) and0-471-48172-6 (Vol 2).

On the aforementioned basis the t_(0.5) for polyetheretherketone at 160°C. (which is close to 15° C. above its Tg) is 126 seconds whichindicates that crystallisation occurs very rapidly.

Said polymeric material suitably has a Tg of greater than 50° C.,preferably greater than 75° C., more preferably greater than 85° C. orgreater than 100° C. Said polymeric material may have a Tg of less than260° C., for example less than 220° C. or less than 200° C. In somecases, the Tg may be less than 190° C., 180° C. or 170° C. Said,polymeric material preferably has a Tg of greater than 50° C., morepreferably greater than 80° C., especially greater than 120° C.

Said polymeric material suitably has a melt viscosity (MV) of at least0.06 kNsm⁻², preferably has a MV of at least 0.08 kNsm⁻², morepreferably at least 0.085 kNsm⁻², especially at least 0.09 kNsm⁻². MV issuitably measured using capillary rheometry operating at 400° C. at ashear rate of 1000 s⁻¹ using a tungsten carbide die, 0.5×3.175 mm. Saidpolymeric material may have a MV of less than 1.00 kNsm⁻², suitably lessthan 0.5 kNsm⁻².

Said polymeric material may have a tensile strength, measured inaccordance with ASTM D790 of at least 40 MPa, preferably at least 60MPa, more preferably at least 80 MPa. The tensile strength is preferablyin the range 80-110 MPa, more preferably in the range 80-100 MPa.

Said polymeric material may have a flexural strength, measured inaccordance with ASTM D790 of at least 145 MPa. The flexural strength ispreferably in the range 145-180 MPa, more preferably in the range145-165 MPa.

Said polymeric material may have a flexural modulus, measured inaccordance with ASTM D790, of at least 2 GPa, preferably at least 3 GPa,more preferably at least 3.5 GPa. The flexural modulus is preferably inthe range 3.5-4.5 GPa, more preferably in the range 3.5-4.1 GPa.

Preferably, said polymeric material has a moiety of formula

and/or a moiety of formula

and/or a moiety of formula

wherein m, r, s, t, v, w and z independently represent zero or apositive integer, E and E′ independently represent an oxygen or asulphur atom or a direct link, G represents an oxygen or sulphur atom, adirect link or a —O-Ph-O— moiety where Ph represents a phenyl group andAr is selected from one of the following moieties (i)**, (i) to (iv)which is bonded via one or more of its phenyl moieties to adjacentmoieties

Unless otherwise stated in this specification, a phenyl moiety has 1,4-,linkages to moieties to which it is bonded.

In (i), the middle phenyl may be 1,4- or 1,3-substituted. It ispreferably 1,4-substituted.

In one embodiment, a polymeric material may comprise a repeat unit offormula I and no other repeat units. Said polymeric material may bepolyphenylenesulphide (PPS).

In a preferred embodiment, said polymeric material may include more thanone different type of repeat unit of formula I; and more than onedifferent type of repeat unit of formula II; and more than one differenttype of repeat unit of formula III. Preferably, however, only one typeof repeat unit of formula I, II and/or III is provided.

Said moieties I, II and III are suitably repeat units. In the polymericmaterial, units I, II and/or III are suitably bonded to one another—thatis, with no other atoms or groups being bonded between units I, II andIII.

Phenyl moieties in units I, II and III are preferably not substituted.Said phenyl moieties are preferably not cross-linked.

Where w and/or z is/are greater than zero, the respective phenylenemoieties may independently have 1,4- or 1,3-linkages to the othermoieties in the repeat units of formulae II and/or III. Preferably, saidphenylene moieties have 1,4-linkages.

Preferably, the polymeric chain of the polymeric material does notinclude a —S— moiety. Preferably, G represents a direct link.

Suitably, “a” represents the mole % of units of formula I in saidpolymeric material, suitably wherein each unit I is the same; “b”represents the mole % of units of formula II in said polymeric material,suitably wherein each unit II is the same; and “c” represents the mole %of units of formula III in said polymeric material, suitably whereineach unit III is the same. Preferably, a is in the range 45-100, morepreferably in the range 45-55, especially in the range 48-52.Preferably, the sum of b and c is in the range 0-55, more preferably inthe range 45-55, especially in the range 48-52. Preferably, the ratio ofa to the sum of b and c is in the range 0.9 to 1.1 and, more preferably,is about 1. Suitably, the sum of a, b and c is at least 90, preferablyat least 95, more preferably at least 99, especially about 100. Suitablyb is at least 20, preferably at least 40, more preferably at least 45.Preferably, a is 20 or less, preferably 10 or less, more preferably 5 orless. Preferably, said polymeric material consists essentially ofmoieties I, II and/or III.

Said polymeric material may be a homopolymer having a repeat unit ofgeneral formula

or a homopolymer having a repeat unit of general formula

or a random or block copolymer of at least two different units of IVand/or Vwherein A, B, C and D independently represent 0 or 1 and E, E′, G, Ar,m, r, s, t, v, w and z are as described in any statement herein.

Preferably, m is in the range 0-3, more preferably 0-2, especially 0-1.Preferably, r is in the range 0-3, more preferably 0-2, especially 0-1.Preferably t is in the range 0-3, more preferably 0-2, especially 0-1.Preferably, s is 0 or 1. Preferably v is 0 or 1. Preferably, w is 0or 1. Preferably z is 0 or 1.

Preferably, said polymeric material is a homopolymer having a repeatunit of general formula IV.

Preferably Ar is selected from the following moieties (xi)** and (vii)to (x)

In (vii), the middle phenyl may be 1,4- or 1,3-substituted. It ispreferably 1,4-substituted.

Suitable moieties Ar are moieties (i), (ii), (iii) and (iv) and, ofthese, moieties (i), (ii) and (iv) are preferred. Other preferredmoieties Ar are moieties (vii), (viii), (ix) and (x) and, of these,moieties (vii), (viii) and (x) are especially preferred.

Said polymeric material suitably includes at least 60 mole %, preferablyat least 70 mole %, more preferably at least 80 mole %, especially atleast 90 mole % of repeat units which do not include —S— or —SO₂—moieties. Said polymeric material suitably includes at least 60 mole %,preferably at least 70 mole %, more preferably at least 80 mole %,especially at least 90 mole % of repeat units which consist essentiallyof phenyl moieties, ether moieties and ketone moieties.

An especially preferred class of polymeric materials are polymers (orcopolymers) which consist essentially of phenyl moieties in conjunctionwith ketone and/or ether moieties. That is, in the preferred class, thepolymeric material does not include repeat units which include —S—,—SO₂— or aromatic groups other than phenyl. Preferred polymericmaterials of the type described include:

-   -   (a) a polymer consisting essentially of units of formula IV        wherein Ar represents moiety (iv), E and E′ represent oxygen        atoms, m represents 0, w represents 1, G represents a direct        link, s represents 0, and A and B represent 1 (i.e.        polyetheretherketone).    -   (b) a polymer consisting essentially of units of formula IV        wherein E represents an oxygen atom, E′ represents a direct        link, Ar represents a moiety of structure (i), m represents 0, A        represents 1, B represents 0 (i.e. polyetherketone);    -   (c) a polymer consisting essentially of units of formula IV        wherein E represents an oxygen atom, Ar represents moiety (i), m        represents 0, E′ represents a direct link, A represents 1, B        represents 0, (i.e. polyetherketoneketone).    -   (d) a polymer consisting essentially of units of formula IV        wherein Ar represents moiety (i), E and E′ represent oxygen        atoms, G represents a direct link, m represents 0, w represents        1, r represents 0, s represents 1 and A and B represent 1. (i.e.        polyetherketoneetherketoneketone).    -   (e) a polymer consisting essentially of units of formula IV,        wherein Ar represents moiety (iv), E and E′ represents oxygen        atoms, G represents a direct link, m represents 0, w represents        0, s, r, A and B represent 1 (i.e. polyetheretherketoneketone).    -   (f) a polymer comprising units of formula IV, wherein Ar        represents moiety (iv), E and E′ represent oxygen atoms, m        represents 1, w represents 1, A represents 1, B represents 1, r        and s represent 0 and G represents a direct link (i.e.        polyether-diphenyl-ether-phenyl-ketone-phenyl-).

The main peak of the melting endotherm (Tm) for said polymeric materialmay be at least 300° C.

Said polymeric material may consist essentially of one of units (a) to(f) defined above.

Said polymeric material preferably comprises, more preferably consistsessentially of, a repeat unit of formula (XX)

where t1, and w1 independently represent 0 or 1 and v1 represents 0, 1or 2. Preferred polymeric materials have a said repeat unit whereint1=1, v1=0 and w1=0; t1=0, v1=0 and w1=0; t1=0, w1=1, v1=2; or t1=0,v1=1 and w1=0. More preferred have t1=1, v1=0 and w1=0; or t1=0, v1=0and w1=0. The most preferred has t1=1, v1=0 and w1=0.

In preferred embodiments, said polymeric material is selected frompolyetheretherketone, polyetherketone, polyetherketoneetherketoneketoneand polyetherketoneketone. In a more preferred embodiment, saidpolymeric material is selected from polyetherketone andpolyetheretherketone. In an especially preferred embodiment, saidpolymeric material is polyetheretherketone.

When said pipe P1 comprises or consists essentially of a polymericcomposition, said polymeric composition may include said polymericmaterial and one or more fillers.

Said polymeric material may make up at least 60 wt %, suitably at least70 wt %, preferably at least 80 wt %, more preferably at least 90 wt %,especially at least 95 wt %, of the total amount of thermoplasticpolymeric materials in said polymeric composition from which said pipeP1 is made.

A single said polymeric material is preferably substantially the onlythermoplastic polymer in said polymeric composition. Suitably, areference to a thermoplastic polymer refers to a polymer which is meltedin the formation of said pipe P1.

A filler is suitably a material which is not melted in manufacture ofpipe P1. It suitably has a melting temperature of greater than 350° C.

Said filler may include a fibrous filler or a non-fibrous filler. Saidfiller may include both a fibrous filler and a non-fibrous filler. Asaid fibrous filler may be continuous or discontinuous. A said fibrousfiller may be selected from inorganic fibrous materials, non-melting andhigh-melting organic fibrous materials, such as aramid fibres, andcarbon fibre. A said fibrous filler may be selected from glass fiber,carbon fibre, asbestos fiber, silica fiber, alumina fiber, zirconiafiber, boron nitride fiber, silicon nitride fiber, boron fiber,fluorocarbon resin fibre and potassium titanate fiber. Preferred fibrousfillers are glass fibre and carbon fibre. A fibrous filler may comprisenanofibres.

A said non-fibrous filler may be selected from mica, silica, talc,alumina, kaolin, calcium sulfate, calcium carbonate, titanium oxide,ferrite, clay, glass powder, zinc oxide, nickel carbonate, iron oxide,quartz powder, magnesium carbonate, fluorocarbon resin, graphite,polybenzimidazole (PBI), carbon powder, nanotubes and barium sulfate.The non-fibrous fillers may be introduced in the form of powder or flakyparticles.

Preferably, said filler comprises one or more fillers selected fromglass fibre, carbon fibre, carbon black and a fluorocarbon resin. Morepreferably, said filler comprises glass fibre or carbon, especiallydiscontinuous, for example chopped, glass fibre or carbon fibre.

Said polymeric composition suitably includes 35-100 wt %, preferably50-100 wt %, more preferably 65-100 wt % of said polymeric material.

Said polymeric composition suitably does not include a reinforcingfiller (e.g. carbon fibre) but may include a non-reinforcing filler(e.g. talc or carbon black) which may be included to reduce costs.However, such a filler could detrimentally increase the roughness of theinside of the pipe and therefore increase pipe losses in the fluidflowing through it. To address this, the inside of the pipe could beprovided (e.g. by coextrusion) with a layer comprising substantially 100wt % of unfilled polymeric material (e.g. the same polymeric material asin said polymeric composition).

Suitably, the total amount of filler in said polymeric composition is 65wt % or less, or 60 wt % or less. Said polymeric composition may include0-65 wt %, preferably 0-50 wt %, more preferably 0-35 wt % of filler.Preferably, said polymeric composition includes less than 5 wt % and,more preferably, includes substantially no filler means. Preferably,said pipe P1 consists essentially of a polymeric material of formula(XX) and, especially, consists essentially of polyetheretherketone.

Said reinforcing means is preferably arranged around substantially theentire outer region and/or outer periphery of pipe P1. It is suitablyarranged to resist mechanical and/or thermal loads to which thecomposite pipe may be exposed in use. For example, it is suitablyarranged to prevent compression of pipe P1 due to the weight of waterthat may act on it in use and/or to resist expansion of pipe P1 due toflow of a hot pressure fluid therethrough in use.

The method may comprise selecting, for use in step (ii) of the method, areinforcing means comprising a first material and a second material.

Said first material may comprise a thermoplastic or thermosetting resin.Said resin may be of any suitable type, for example a polyamide,polysulphone, polyetherimide, polyethersulphone or any of the polymericmaterials comprising (a) phenyl moieties; (b) ketone and/or sulphonemoieties; an/or (c) ether and/or thioether moieties described above forpipe P1. Preferably, said first material is selected from homopolymersor copolymers comprising units IV and/or V referred to above. Morepreferably, said first material is of general formula (XX) as describedabove. Said first material preferably comprises polyetheretherketone.Preferably, the polymeric material of the outer region of pipe P1 andsaid first material are polymeric materials with the same repeat units,for example both being homopolymers or copolymers comprising units IVand/or V and/or being of general formula (XX).

Said second material of said reinforcing means preferably comprises afibrous material. Said fibrous material may independently have anyfeature of the fibrous filler described above in the context of filleroptionally included in pipe P1. Said fibrous material may be continuousor discontinuous. It is preferably selected from glass, aramid or carbonfibres.

Said reinforcing means may include 25-75 wt % (more preferably 35-75 wt%) of said first material and 25-75 wt % (more preferably 25-65 wt %) ofsaid second material.

Said reinforcing means may comprise a substantially homogenousarrangement of said first and second materials.

The reinforcing means selected for step (ii) is preferably flexible andarranged to be wrapped around pipe P1. It may be elongate and it maycomprise a tape, mat or woven structure which is arranged to be woundaround pipe P1.

The reinforcing means may be heated prior to, during and/or after it hasbeen contacted with the pipe P1 in the method. It may be heated to atemperature such that the first material is above its Tg and/or itsoftens or preferably melts. It may be heated to a temperature in therange 330° C. to 400° C. It may be heated using any suitable heatingmeans, for example infra-red, laser, gas flame, hot air or hot gas.Preferably, the first material is in a melted state at some stage aftercontact with pipe P1, suitably so the reinforcing means can bond to pipeP1.

In a first embodiment, said reinforcing means may be extruded as asheath over the selected pipe P1 in the method. Heat from the extrudatewill during and/or after being overlaid on the pipe P1 be transferred tothe pipe P1 to cause the crystallinity of the outer region of pipe P1 toincrease. The reinforcing means for such an embodiment may comprise apolymer of formula (XX), for example polyetheretherketones, and glassfibres for example 20-40 wt % glass fibres.

In other embodiments, said reinforcing means may be flexible and may bewrapped round the pipe P1. For example, in a second embodiment, thereinforcing means may comprise co-mingled fibres comprising said firstand second materials. Said first material, for example ofpolyetheretherketones, may be in the form of a discontinuous fibre (e.g.relatively short fibres of less than 10 mm) and said second material maycomprise continuous fibres, for example of carbon fibre. Such areinforcing means, suitably in the form of a fabric, may be arrangedaround pipe P1 and consolidated by heat and/or pressure. Duringconsolidation, said first material may melt and heat may pass from thefirst material to the pipe P1 to cause the crystallinity of the outerregion of the pipe to increase.

In a third embodiment, said reinforcing means may comprise a firstmaterial defining a matrix in which a fibrous material is arranged. Thematrix suitably comprises a said polymeric material, for example offormula (XX).

Said fibrous material may comprise a fibrous material as describedherein but is preferably selected from glass, aramid and carbon fibres.The fibrous material may be continuous or discontinuous. Saidreinforcing means may comprise a fabric, tape or tow.

Said third embodiment, especially wherein the reinforcing means is inthe form of a tape, is especially preferred.

Said reinforcing means may define a reinforcing layer around pipe P1 ofa thickness of at least 0.25 mm, at least 0.5 mm or at least 1 mm. Thethickness may be in the range 1 mm to 80 mm, for example 1 mm to 50 mm.The reinforcing layer may itself comprise many layers (e.g. greater than10, 25, 40, 70 or 90 layers) of reinforcing means, for example tape,overlaying one another.

In step (ii) of the method, crystallinity of the outer region of pipe P1is caused to increase by subjecting the outer region of pipe P1 to heat,suitably so the outer region can re-crystallise, thereby to increase itscrystallinity. In a preferred embodiment, in step (ii), at least part ofthe outer region of the pipe P1 melts. Thus, preferably, in step (ii),the outer region of the pipe P1 is subjected to a temperature above themelting temperature (Tm) of said polymeric material of pipe P1. However,it should be noted that the crystallinity of regions of pipe P1 mayincrease by being subjected to heat, even though such regions do notmelt. This is discussed hereinafter with reference to FIG. 5.Preferably, in step (ii), heat is conducted from the reinforcing meansto the outer region of pipe P1. Such conduction of heat suitably causescrystallinity of pipe P1 to increase. Preferably, pipe P1 is not heatedby a heating means other than by contact with said reinforcing means orby a heating means used to heat the reinforcing means during or afterapplication of the reinforcing means to the pipe P1.

In step (ii), the crystallinity of an outer surface of pipe P1 mayincrease by at least 2%, suitably by at least 5%, preferably by at least8%, more preferably by at least 10%, especially by at least 12%. Afterstep (ii), the difference between the crystallinity of the outer surfaceof pipe P1 and an inside surface of pipe P1 (preferably between radiallyspaced apart outside and inside surfaces) is less than 5%, suitably lessthan 4% or 3%. After step (ii) the outer surface of pipe P1 may have acrystallinity of at least 20% or at least 25%. The inside surfacepreferably has a crystallinity of at least 20% or at least 25% or atleast 27%.

Said method is a method of producing a flexible riser having a length ofat least 10 m, suitably at least 50 m, preferably at least 100 m, morepreferably at least 500 m, especially at least 1000 m.

The method may involve application of additional layers after step (ii).Such layers may be arranged to protect the reinforcing means.

Preferably, the method is a method of producing a composite pipe whichcomprises a pipe P2 which is produced from said pipe P1 in the method byincreasing the crystallinity of the outer region in step (ii). Thecomposite pipe is described further according to the second aspect.

According to a second aspect of the invention, there is provided acomposite pipe comprising a pipe P2 having an outer region comprising apolymeric material having a crystallinity of greater than 25%, said pipeP2 being overlaid with a reinforcing means, wherein said polymericmaterial includes:

(a) phenyl moieties;

(b) ether and/or thioether moieties and, optionally,

(c) ketone and/or sulphone moieties.

The composite pipe of the second aspect may have any feature of thecomposite pipe produced in the method of the first aspect. In this casepipe P2 represents pipe P1 after its crystallinity has been increased instep (ii) of the method.

A preferred composite pipe has a length of at least 10 m, suitably atleast 50 m, preferably at least 100 m, more preferably at least 500 m,especially at least 1000 m. A preferred pipe comprises a pipe P2comprising, preferably consisting essentially of, a polymeric materialof formula (XX), especially polyetheretherketone, having an insidesurface having a crystallinity of at least 20%, preferably at least 25%;and an outside surface having a crystallinity of at least 20%,preferably at least 25%. The pipe P2 is suitably overlaid with areinforcing means which comprises a polymeric material of formula (XX),especially polyetheretherketone. The reinforcing means preferablyincludes fibres, for example carbon fibre, glass fibre or aramid fibre.The reinforcing means preferably contacts the pipe P2 and polymericmaterial of the reinforcing means is preferably fused and/or mingleswith polymeric material of pipe P2. Thus, preferably no adhesive orother intermediate material is positioned between pipe P2 and thereinforcing means to secure the reinforcing means and pipe P2 together.A protective layer suitably extends around the reinforcing means.

The composite pipe may have an outside diameter of at least 5 cm, 10 cm,20 cm, 30 cm or 40 cm. The outside diameter may be less than 100 cm,less than 90 cm, less than 80 cm, less than 70 cm, or less than 60 cm.

The composite pipe is preferably flexible enough to be spooled onto areel with a hub radius of 4500-8500 mm.

The invention extends to a flexible riser for transporting fluid betweena floating production unit and a sub-sea wellhead. The riser maycomprise a composite pipe made as described in the first aspect and/oras described in the second aspect. The flexible riser preferablyincludes means for connection to the sub-sea well head and/or means forconnection to the floating production unit.

According to a third aspect of the invention, there is provided a methodof transporting fluid between first and second locations, the methodcomprising positioning a composite pipe as described herein between thelocations.

The first location may be sub-surface, for example a sub-sea location.The second location may be above the height of the first location, forexample it may be arranged at/or adjacent the surface of the sea and maycomprise a floating production unit.

The composite pipe may define a lazy S-shape.

According to a fourth aspect, there is provided an assembly comprising acomposite pipe secured between first and second locations, for examplebetween a sub-sea wellhead and a production unit.

The composite pipe may define a lazy S-shape.

The invention extends to the use of a composite pipe as described hereinfor transporting fluids between first and second locations as describedherein.

Any invention described herein may be combined with any feature of anyother invention or embodiment described herein mutatis mutandis.

Specific embodiments of the invention will now be described, by way ofexample, with reference to the accompanying figures in which:

FIG. 1 is a cross-section through a composite pipe;

FIG. 2 is a cross-section through an apparatus for producing apolyetheretherketone (PEEK) pipe having an amorphous skin;

FIG. 3 is a cross-section through a PEEK pipe having an amorphous skin;

FIG. 4 is a plot of % crystallinity v. distance from surface for thePEEK pipe of FIG. 3; and

FIG. 5 is a schematic representation of the through wall temperaturedistribution of the PEEK pipe during bonding of a carbon fibre/PEEKcomposite reinforcing tape to the PEEK.

A composite pipe, shown in FIG. 1, comprises a polyetheretherketone(PEEK) innermost pipe 2 around which a reinforcing overwrap 4 isarranged. A protective sheath 5 surrounds the overwrap 4. The pipe has asubstantially constant cross-section along its extent.

The pipe 2 contacts fluids (e.g. oil and/or gas) flowing therewithin inuse and must be able to withstand the temperature of such fluids(typically 100-200° C.), be chemically inert to such fluids and resistwear and abrasion so that the pipe 2 can enjoy a long service life. PEEKsatisfies the aforementioned requirements. It has high temperatureresistance, allowing long term use at a temperature in excess of 200° C.It also has high chemical resistance, high permeation resistance andhigh erosion/wear resistance. It also can readily be arranged to definea relatively smooth bore 7, which facilitates passage of fluidstherethrough. Additionally, the pipe can have high enough strength toenable it to act as a mandrel during application, for example winding,of overwrap 4.

The reinforcing overwrap 4 is arranged to tolerate and/or resistmechanical loads, to which the composite pipe may be exposed in use. Forexample, the reinforcing overwrap 4 is arranged to resist expansion ofthe pipe 2 due to the pressure of fluids flowing therewithin;compression of pipe 2 due to external pressure, for example whenpositioned in deep water; tension from its own hanging weight; andfatigue by action of wave motion or other movement.

The reinforcing overwrap 4 is defined by a flat tape which comprisesunidirectional continuous or jointed fibres of carbon, glass and/oraramid embedded in a PEEK matrix which is wrapped around the pipe 2. Thefibre volume in the tape is typically 20-70 vol %, with the PEEK matrixproviding the remaining 30 to 80 vol %. Suitable tape is available fromTen Cate Advanced Composites USA, Inc. or from Suprem.

The protective sheaf 5 may comprise a relatively cheap polymericmaterial which has a relatively low melting point such as polyethylene,polyamide (e.g. polyamide 11 or 12) or polyurethane.

The composite pipe may be manufactured as described further below.

The innermost pipe 2 is made by extruding an annular section moltentube, followed by cooling and solidification to produce a continuouspipe. Referring to FIG. 2, the cooling process may be carried out bypassing the extruded melted PEEK 5 through the centre of a brass sleeve6, typically of wall thickness 2-3 mm which is immersed within a waterbath 8. A vacuum is applied to the interior of the water bath to drawthe extrudate out so that it touches the brass sleeve, the resultingheat transfer between extrudate and sleeve leading to solidification ofthe PEEK. The vacuum may be generated using a liquid-ring-seal type ofvacuum pump, an internal water overflow in the tank being the supply tothe pump. The brass sleeve 6 has openings 10 which allow air trappedbetween the extrudate (and forming pipe 12) and the brass sleeve toescape.

Whilst PEEK crystallises quickly, water quenching can result in rapidcooling such that the crystallisation process is inhibited. Thus, waterquenching of the melted PEEK in the process results in the formation ofa PEEK pipe as shown in FIG. 3 which has a skin 14 which is relativelyamorphous and an inner region 16 which is relatively crystalline. FTIRmay be used to assess crystallinity and this may be used to assess thelevel of crystallinity at a surface and/or across the thickness orsurface of a sample. Reference is made to a paper titled “Crystallinityin Poly(Aryl-Ether-Ketone) Plaques Studied by Multiple InternalReflection Spectroscopy” (Polymer Bull, 11, 433 (1984)). Typically, theamorphous skin is found to be 100-200 μm in depth and has acrystallinity of less than 15%. There is quite a sharp transitionbetween the amorphous skin 14 and the interior 16. Typically, the latterhas a crystallinity of 27% or greater.

As a result of the formation of the skin and the regions of differentcrystallinities, the PEEK pipe has high through-wall stress meaning thatit would be susceptible to early failure, for example cracking, if itwas subjected to high forces, for example as a result of bending or widetemperature fluctuations, in use. FIG. 4 shows the % crystallinityacross the pipe and illustrates the significantly wide variation incrystallinity leading to stresses within the pipe wall. It will be notedthat the highest crystallinity is seen in a region slightly outwardly ofthe inside surface. This is the region which cools slowest, duringmanufacture of the pipe. It will be appreciated that there will be someloss of heat from the inside surface itself and a slightly lower rate ofloss of heat from the region adjacent the inside surface.

The reinforcing overwrap 4 is built up by winding the PEEK/fibre tape onthe pipe 2 to define a hundred or more layers of tape. Since PEEK is athermoplastic, with no significant tackiness to facilitate bonding ofthe PEEK in the tape to the PEEK in the pipe 2, the tape may be appliedunder tension and the tension maintained until heat is applied to meltthe tape and consolidate it and hold it in place. Alternatively, andpreferably, the tape may be heated and consolidated as it comes intocontact with the PEEK of the pipe 2. Such localised heating of the tapeas it meets the pipe 2 may be achieved using a heat source such asinfra-red, laser, gas flame, hot air or hot gas. The tape is thenconsolidated by using a following roller.

As a result of the heat applied to the tape, the PEEK in it melts and,additionally, the surface of the pipe 2 may be melted and willsubsequently re-solidify. Since the surface 14 of pipe 2 is amorphous,the application of the heat causes re-crystallisation. As a result, thecrystallinity of the skin 14 is increased to a similar level to that ofthe interior adjacent thereto, so that there is no longer a defined skinbut rather a substantially constant crystallinity from the outside wallof pipe 2 to the inside wall of the pipe 2. As a result, stress withinthe pipe 2 is substantially removed, after the tape has been applied.

FIG. 5 includes a representation of the temperature distribution duringbonding of the tape to the PEEK pipe. The figure represents temperatureof the pipe 2 on the y axis and the pipe wall thickness on the x axis,with the outside surface of the pipe being represented at the left handside of the x axis and the inside surface being represented at the righthand side of the x axis. During the process of welding the tape to thepipe 2, the surface of pipe 2 will melt in a zone defined as the meltzone in FIG. 4. It will subsequently slowly re-crystallise as itsolidifies since it is cooled relatively slowly due to it beingsubjected to ambient conditions and being insulated by the tape. Thus,its crystallinity will rise towards a typical level for a pipe made fromPEEK. The temperature profile across the wall of pipe 2 duringapplication of the tape is illustrated by line 30 in FIG. 4. As will beappreciated, the inside surface of the pipe wall is not significantlyheated during application of the tape. Inwards of the melt zone, thereis a further zone where further re-crystallisation occurs. This zone isdefined by the intersection (at point 34) of the temperature profileline 30 and a “temperature of manufacture” line 32. The latter refers tothe maximum temperature to which pipe 2 is subjected during its coolingin the apparatus of FIG. 2. It is understood that, in general,re-crystallisation of pipe 2 will only occur in regions which aresubjected to a temperature during application of the tape which ishigher than the temperature to which the regions were subjected duringtheir manufacture in the cooling apparatus of FIG. 2. As a result of there-crystallisation, the amorphous skin 14 of the pipe becomescrystalline (e.g. having a crystallinity of more than 25% and thecrystallinity across the wall of pipe 2 becomes substantially constant.

After application of overwrap 4, the protective sheaf 5 may be appliedin an extrusion process.

The composite pipe may be produced in very long lengths for example of1000 m or more. It is preferably arranged to be spooled on a reel and,therefore, must be sufficiently flexible. The reduction of stresseswithin pipe 2 by use of the process described makes the pipe 2 lesssusceptible to failure and therefore advantageously extends its usefullifetime.

The composite pipe is preferably a flexible riser arranged to transportfluids between floating production units and a sub-sea wellhead.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

The invention claimed is:
 1. A method of producing a composite pipewhich comprises: (i) selecting a pipe P1 having an outer regioncomprising a crystalline or crystallisable polymeric material having acrystallinity of less than 25%, wherein said polymeric materialincludes: (a) phenyl moieties; (b) ether and/or thioether moieties; and,optionally, (c) ketone and/or sulphone moieties; and (ii) overlaying theselected pipe P1 with a reinforcing structure and causing thecrystallinity of the outer region of pipe P1 to increase, thereby todefine the composite pipe.
 2. The method according to claim 1, whereinsaid crystallinity of the outer region in step (i) is less than 15%. 3.The method according to claim 1, wherein substantially the entirety ofthe periphery of the pipe has said crystallinity of less than 25%. 4.The method according to claim 1, wherein the thickness of the wall whichdefines the pipe P1 is at least 0.5 mm and less than 30 mm.
 5. Themethod according to claim 1, wherein said outer region has a thicknessof at least 50 μm.
 6. The method according to claim 1, wherein the ratioof the thickness of the outer region to the thickness of the annularwall which defines pipe P1 is in the range 0.01 to 0.2.
 7. The methodaccording to claim 1, wherein an inwardly facing surface of the pipe hasa crystallinity which is greater than the crystallinity of said outerregion by at least 2%.
 8. The method according to claim 7, wherein thecrystallinity of said inwardly facing surface is at least 4% more thanthe crystallinity of the outer region of pipe P1 selected in step (i) ofthe method.
 9. The method according to claim 1, wherein thecrystallinity half-life of the polymeric material at 15° C. above its Tgis less than 1000 seconds.
 10. The method according to claim 1, whereinsaid polymeric material has a moiety of formula of at least one of:

wherein m, r, s, t, v, w and z independently represent one or zero and apositive integer, E and E′ independently represent an oxygen or asulphur atom or a direct link, G represents an oxygen or sulphur atom, adirect link or a —O-Ph-O— moiety where Ph represents a phenyl group andAr is selected from one of the following moieties (i)**, (i) to (iv)which is bonded via one or more of its phenyl moieties to adjacentmoieties


11. The method according to claim 1, wherein said polymeric materialcomprises a repeat unit of formula (XX)

where t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or2.
 12. The method according to claim 11, wherein said pipe P1 consistsessentially of a polymeric material of formula (XX).
 13. The methodaccording to claim 1, wherein said polymeric material ispolyetheretherketone.
 14. The method according to claim 1, wherein saidreinforcing structure is arranged around substantially at least one ofthe entire outer region and the outer periphery of pipe P1.
 15. Themethod according to claim 1, the method comprising selecting for thereinforcing structure a first material and a second material, whereinsaid first material comprises one of a thermoplastic and a thermosettingresin.
 16. The method according to claim 1, wherein said reinforcingstructure is heated at least one of prior to, during, and after it hasbeen contacted with pipe P1 and is heated to a temperature such that thefirst material is at least one of above its Tg and softens and melts.17. The method according to claim 1, wherein in step (ii), crystallinityof the outer region of pipe P1 is caused to increase by subjecting theouter region of pipe P1 to heat so the outer region can re-crystallise,thereby to increase its crystallinity.
 18. The method according to claim1, wherein after step (ii), the difference between the crystallinity ofthe outer region of pipe P1 and an inside surface of pipe P1 is lessthan 5%.
 19. The method according to claim 1, wherein the methodproduces a flexible riser having a length of at least 10 m.